Going back and forth through the Main Timeline

Dear all,

I'm working on a HTML5 canvas.

I have two buttons.

By clicking on the first button (BUTTON 1) I go to the next fifth frame and stop there.

By clicking the other button (BUTTON 2) I go back to the first frame (number 0) wherever currentframe the animation is.

Actually, I used this codes:

BUTTON 1:

exportRoot.BUTTON 1.addEventListener("click", fl_ClickToGoToAndStopAtFrame_1.bind(this));
function fl_ClickToGoToAndStopAtFrame_1() {
    exportRoot.gotoAndStop(exportRoot.currentFrame + 5);
}

BUTTON 2:

exportRoot.BUTTON 2.addEventListener("click", fl_ClickToGoToAndStopAtFrame_2.bind(this));
function fl_ClickToGoToAndStopAtFrame_2() {
    exportRoot.gotoAndStop(0);
}

However it happens that when I click on BUTTON 2 it's ok: the animation goes to frame 0

BUT

afterwards, if I newly click on BUTTON 1 it skips several frames: it does not go to frame 5.

What happens?

Do I have to reset the timeline when I go back to frame 0?

I don't really know what happens

Thank you in advance